1. Field of the Invention
The present invention relates to a method and apparatus for message correction, and more particularly to a receiver and method for correcting received message information.
2. Description of the Related Art
When transmitting a predetermined language character (e.g., a matrix character which may be a kana character (a Japanese language character) or the like) as message information to a receiver, a caller inputs a character conversion code for a character (e.g., a kana character) and then inputs the numerical data corresponding to the specific kana character, to transmit the character. A two-digit character is used for one character according to the character conversion matrix shown in FIG. 15. When there is a character conversion code in a received message, the receiver converts the numerical data into characters according to a character conversion matrix, and displays the message information on a display section in the form of characters.
Such a receiver normally cannot display a message if an error occurs in the transmission path. Therefore, a conventional receiver having a message correction mechanism is provided within a memory (i.e., a random access memory (RAM)) storing many pieces of message information relating to common errors that are previously input. Such a system is shown by the individual calling system disclosed in Japanese Patent Application Laid-Open No. 244065/1993. The receiver decides whether an error occurs in the received message data according to BCH (e.g., Bose Chaudhuri Hocquenghem) parity bits. The BCH parity bit may be an error correct bit of, for example, ten bits. It is used to check for errors. It can detect one error bit generated during the communication process, and it is sent as a portion of the message data.
When the presence or possibility of an error exists, the conventional receiver searches the information coinciding with, or similar to, the received message information within the RAM, and displays the searched information together with the received message information. The above structure also confirms whether there is an error in a received message. The conventional system confirms the error according to the BCH parity bit in the received message data. If the received message data has more than two errors, the conventional system compares it with predetermined message data in the RAM.
More specifically, in Japanese Patent Application Laid-Open No. 187742/1988, a newly-received message A is compared with a message B previously stored in memory. When certain conditions are satisfied (e.g., such as the number of characters of message A equaling that of message B, the characters (excluding the characters detected as errors by BCH parity bits) in message A coinciding with those in message B, and the number of mismatched characters in messages A and B being equal to or less than a predetermined rate of all characters), then message A is detected as a re-received message (i.e., a duplicate) of message B. Further, a character detected as an error in either of messages A or B is replaced with a character not detected as an error, thereby to obtain a correct message.
A radio selective-calling receiver with a display function is disclosed in Japanese Patent Application Laid-Open No. 198931/1986. In such a system, a received message is error-checked by an arithmetic logic unit (ALU), and is temporarily stored in a sub-storing section in the RAM. The characters in the temporarily stored message are compared one by one with the characters in messages previously stored in the main storing section in the RAM. When all pairs of characters free from error are identical, characters with errors in the messages in the main storing section are corrected, thereby to obtain a message with less errors. Once duplicate messages are found in the RAM, the method used to correct the errors is similar to the previously-mentioned prior art reference (e.g., Japanese Patent Application Laid-Open No. 187742/1988). Specifically, this system confirms the error with comparing a received message with a message previously stored in the RAM.
A problem arises in Japanese Patent Application Laid-Open No. 244065/1993, in that a large amount of information must be input previously into the RAM, so that many different types of errors can be corrected. However, regardless of the amount of corrective information input to the RAM, all errors cannot corrected because it is impossible to input all possible error patterns in the RAM.
In Japanese Patent Application Laid-Open No. 187742/1988, a problem occurs when the same error exists in both messages A and B because the portions cannot be replaced with each other.
Additionally, in Japanese Patent Application Laid-Open No. 198931/1986, a problem occurs when the error check portion of a received message contains the same errors as that of a message previously stored in the main storing section in a RAM. In such a case, it is impossible to correct the error portion of the message in the main storing section.
Moreover, the above conventional systems only correct errors that occur in the communication route. No system corrects errors due to an incorrect input by a caller. For example, when a caller forgets to input a character conversion code or confuses the input of the data, a correct character conversion cannot be performed. Therefore, a nonsense message may be transmitted which does not include the contents to be transmitted by the caller.
FIGS. 12(a), 12(b), 12(d) and 12(e) and 13(a), 13(b), 13(e), and 13(f) illustrate some incorrect inputs. For example, FIG. 12(a) shows when a caller neglects to input a character conversion code. In such a case, the character is not converted into a character but it is directly displayed (e.g., see FIG. 12(b)).
FIGS. 12(d) and 13(a) show when the numerical data input after a character conversion code includes one extra character or is missing a character, and FIG. 13(e) shows when the numerical data after a character conversion code is duplicated.
Regardless, because every two characters are converted into characters according to a character conversion matrix, the splitting of one character could occur, and a nonsense message could be generated (e.g., see FIG. 12(e) and FIGS. 13(b) and 13(f)).